1. Field of the Invention
The present invention relates to an imaging unit and a coin identifying apparatus.
Priority is claimed on Japanese Patent Application No. 2011-076340, filed Mar. 30, 2011, the content of which is incorporated herein by reference.
2. Description of Related Art
There is known a coin identifying apparatus that images a surface of a coin, and identifies the coin from the unevenness pattern of the coin surface that appears in the acquired image. That kind of coin identifying apparatus successively conveys a plurality of coins on a conveyance route, and when the coins pass an imaging location that is provided on that conveyance route, that coin is imaged by the imaging unit. That imaging unit includes a light source that emits illumination light that illuminates the coin surface, and an imager that receives the reflected light that is reflected by the coin surface (see, for example, Japanese Unexamined Patent Application, First Publication No. H09-319911 (hereinbelow referred to as Patent Document 1) and Japanese Unexamined Patent Application, First Publication No. H06-150104 (hereinbelow referred to as Patent Document 2)).
In the imaging unit that is disclosed in Patent Document 1, the light source is arranged away from the normal direction of the coin surface, and the imager is arranged in the normal direction of the coin surface. The illumination light that is emitted from the light source is obliquely incident on the coin surface, and the imager mainly receives the reflected light that is reflected by the edge portion of the unevenness pattern of the coin surface. Contrast is generated between the edge portion of the unevenness pattern of the coin surface and the other portion in the image that is obtained by this imaging unit. However, since this imaging unit receives by the imaging unit the reflected light that has been reflected at the edge portion of the unevenness pattern of the coin surface, it is difficult to detect the defaced state and color of the coin surface.
In the imaging unit that is disclosed in Patent Document 2, a surface light source that emits parallel light is used as the light source. The surface light source is arranged in the normal direction of the coin surface. A half mirror is arranged between the surface light source and the coin. An imager is arranged in the optical path of the light beam that advances in the normal direction of the coin surface and is reflected by the half mirror. The illumination light (parallel light) that is emitted from the surface light source passes through the half mirror to be perpendicularly incident on the coin surface. The imager receives the reflected light that is mainly reflected by the coin surface excluding the edge portion of the unevenness pattern, and reflected by the half mirror. Contrast is generated between the edge portion of the unevenness pattern of the coin surface and the other portion in the image that is obtained by this imaging unit. Moreover, it is also possible to detect the defaced state and color of the coin surface with this imaging unit.
However, in the imaging unit that is disclosed in Patent Document 2, in the case of the defacement of the coin surface being severe, or the coin surface being a diffusing surface, the brightness of the coin surface is overall insufficient. As a result, the contrast between the edge portion of the unevenness pattern and the other portion of the coin surface in the acquired image becomes indistinct, and identification sometimes cannot be performed. As a solution in such a case, adjusting the output of the light source in accordance with the nature of the coin surface leads to a drop in the identification process speed in a coin identifying apparatus that images a plurality of coins in succession.